Source file src/pkg/math/bits.go

     1	// Copyright 2009 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package math
     6	
     7	const (
     8		uvnan    = 0x7FF0000000000001
     9		uvinf    = 0x7FF0000000000000
    10		uvneginf = 0xFFF0000000000000
    11		mask     = 0x7FF
    12		shift    = 64 - 11 - 1
    13		bias     = 1023
    14	)
    15	
    16	// Inf returns positive infinity if sign >= 0, negative infinity if sign < 0.
    17	func Inf(sign int) float64 {
    18		var v uint64
    19		if sign >= 0 {
    20			v = uvinf
    21		} else {
    22			v = uvneginf
    23		}
    24		return Float64frombits(v)
    25	}
    26	
    27	// NaN returns an IEEE 754 ``not-a-number'' value.
    28	func NaN() float64 { return Float64frombits(uvnan) }
    29	
    30	// IsNaN returns whether f is an IEEE 754 ``not-a-number'' value.
    31	func IsNaN(f float64) (is bool) {
    32		// IEEE 754 says that only NaNs satisfy f != f.
    33		// To avoid the floating-point hardware, could use:
    34		//	x := Float64bits(f);
    35		//	return uint32(x>>shift)&mask == mask && x != uvinf && x != uvneginf
    36		return f != f
    37	}
    38	
    39	// IsInf returns whether f is an infinity, according to sign.
    40	// If sign > 0, IsInf returns whether f is positive infinity.
    41	// If sign < 0, IsInf returns whether f is negative infinity.
    42	// If sign == 0, IsInf returns whether f is either infinity.
    43	func IsInf(f float64, sign int) bool {
    44		// Test for infinity by comparing against maximum float.
    45		// To avoid the floating-point hardware, could use:
    46		//	x := Float64bits(f);
    47		//	return sign >= 0 && x == uvinf || sign <= 0 && x == uvneginf;
    48		return sign >= 0 && f > MaxFloat64 || sign <= 0 && f < -MaxFloat64
    49	}
    50	
    51	// normalize returns a normal number y and exponent exp
    52	// satisfying x == y × 2**exp. It assumes x is finite and non-zero.
    53	func normalize(x float64) (y float64, exp int) {
    54		const SmallestNormal = 2.2250738585072014e-308 // 2**-1022
    55		if Abs(x) < SmallestNormal {
    56			return x * (1 << 52), -52
    57		}
    58		return x, 0
    59	}